<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>判断闰年</title>
</head>
<body>
  <script>
    let year=+prompt('请输入年份：')
    if((year % 4===0 && year % 100 !==0)||year % 400===0){
      alert('是闰年')
    }
    else{
      alert('是平年')
    }
  </script>
</body>
</html>